. Compendium of meteorology. Meteorology. 3 4 5 6 DIAMETER OF RAINDROPS (MM) Fig. 1.—Ratio of true scattering to Rayleigh scattering. by Haddock (unpublished) from calculations made by the National Bureau of Standards. For a wave length of 10 cm, Rayleigh scattering holds almost exactly. Table I. Radar Cross Section (<r) for Various Rain Intensities (in 10~' cm^ per cubic centimeter) Rainfall X = cm x = 3 cm (mm hr') Ryde Haddock Ryde Haddock 162 176 25 390 415 50 901 968 4
. Compendium of meteorology. Meteorology. 3 4 5 6 DIAMETER OF RAINDROPS (MM) Fig. 1.—Ratio of true scattering to Rayleigh scattering. by Haddock (unpublished) from calculations made by the National Bureau of Standards. For a wave length of 10 cm, Rayleigh scattering holds almost exactly. Table I. Radar Cross Section (<r) for Various Rain Intensities (in 10~' cm^ per cubic centimeter) Rainfall X = cm x = 3 cm (mm hr') Ryde Haddock Ryde Haddock 162 176 25 390 415 50 901 968 100 2000 1920 148 139 150 3130 2890 289 238 Table I gives the radar cross section for different rain intensities based on the mean drop-size distribution of Laws and Parsons [6], as computed separately by Ryde and Haddock. In view of the complexity of the computations, the disagreement is not surprising. Refraction In passing through the atmosphere the radio waves are subject to refraction and thereby travel a curved path. The curvature of the ray is stronger the greater the gradient of the refractive index perpendicular to its path (the ray tends to curve towards higher re- fractive index). In a standard atmosphere of 60 per cent relative humidity the curvature of the ray in the lowest few kilometei's of the atmosphere is about one-quarter the curvature of the earth. In tropical regions the curva- ture is greater; in Florida during summer it averages about 40 per cent of the earth's curvature. In regions where the vapor pressure decreases rapidly with elevation through a temperature inversion, such as over the trade wind regions of the subtropical high, the curvature of the ray is greater than that of the earth. In such cases the rays, initially nearly horizontal with the earth's surface, may be said to be "trapped" within a narrow layer along the earth and the radar detection of objects near the surface may extend to ab- normally long ranges. Generally, howeve
Size: 1470px × 1700px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectmeteorology
